HackerRank Palindromes

题目在这里

https://www.hackerrank.com/challenges/palindromes

用到了高斯消元

#include "stdio.h"
#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <algorithm>
#include "string.h"
using namespace std;
double Matrix[1000][1000];
string Normalize(string s){
	string res;
	int num[26],val=0;
	memset(num,-1,sizeof(num));
	for(int i=0;i<s.size();i++){
		if(num[s[i]-'a']==-1)
			num[s[i]-'a']=val++;
		res.push_back(('a'+num[s[i]-'a']));
	}
	return res;
}
map<string,int> ids;
map<string,double> ans;
double solve(string s){
	s=Normalize(s);
	if(ans.find(s)!=ans.end())
		return ans[s];

	ids.clear();
	string next=s;
	sort(next.begin(),next.end());
	do{
		string next_s=Normalize(next);
		if(ids.find(next_s)==ids.end()){
			int size=ids.size();
			ids[next_s]=size;
		}

	}while(next_permutation(next.begin(),next.end()));

	int N=ids.size(), len=s.size(), swapSize=len*(len-1)/2;
	for(int i=0;i<=N;i++)
		for(int j=0;j<=N;j++)
			Matrix[i][j]=0;
	for(map<string,int>::iterator it=ids.begin();it!=ids.end();it++){
		string str=it->first;
		int id=it->second;
		if(Matrix[id][N]!=0) continue;
		Matrix[id][N]=Matrix[id][id]=1;
		string tmp=str;
		reverse(tmp.begin(),tmp.end());
		if(tmp==str){
			Matrix[id][N]=0;
			continue;
		}
		for(int i=0;i<len;i++){
			for(int j=i+1;j<len;j++){
				swap(str[i],str[j]);
				int id2=ids[Normalize(str)];
				Matrix[id][id2]-=1.0/swapSize;
				swap(str[i],str[j]);
			}
		}
	}

	for(int i=0;i<N;i++){
		for(int j=N;j>=i;j--) Matrix[i][j]/=Matrix[i][i];
		for(int j=0;j<N;j++){
			if(i!=j){
				for(int k=N;k>=i;k--)
					Matrix[j][k]-=Matrix[i][k]*Matrix[j][i];
			}
		}
	}

	for(map<string,int>::iterator it=ids.begin();it!=ids.end();it++){
		string str=it->first;
		int id=it->second;
		if(ans.find(str)==ans.end())
			ans[str]=Matrix[id][N];

	}
	return ans[s];
}
int main(){
	int T;
	scanf("%d",&T);
	for(int t=0;t<T;t++){
		string str;
		cin>>str;
		printf("%.4lf\n",solve(str));
	}
}